I was surprised that you cannot donate less than a pint of blood. I wanted to donate but that put me off, one pint is too much lost blood in one sitting. I wonder why these restrictions and why not allow people to donate half of that for example. Is it just for convenience for blood collectors?

It's because blood bags are typically pre-filled with a measured dose of an anticoagulant to increase how long the blood can be stored. If they're only partially filled there will be too much anticoagulant for the volume of blood.

I believe the most common anticoagulant used today is Citrate Phosphate Dextrose Adenine Solution (CPDA-1), which doesn't have a Wikipedia page, but it's mentioned on the page for the the older acid-citrate-dextrose:

https://en.wikipedia.org/wiki/Acid-citrate-dextrose

However, I agree that volumes of blood per donation (which varies by country) are sometimes so big that it probably discourages many potential donors. It's possible that demanding such a large quantity from each donor reduces the total amount of blood donated.

Off the top of my head, I imagine blood bag sizes are standardized, so they're easy to deal with during an emergency transfusion.

It would be a nightmare to deal with containers with mixed volumes of blood. "This patient needs 3 litres of O-, let me figure out which combination of blood bags do I need now"

Donated blood is not used directly like that.

It is indeed tested and mixed.

That's why they ask so many questions about your risk of disease when donating.

I didn't know it was mixed, thanks for the clarification. I guess it makes sense to mix it.

> I wanted to donate but that put me off, one pint is too much lost blood in one sitting.

What do you mean?

You do you, but I'm pretty athletic, donate blood frequently, and have never really noticed any degradation in my athletic performance the day after a donation. Unless you have some medical condition, the standard amount is no big deal.